in 2018 the obama care will start taxing the very highest premiums, the cadillac plans. anything over that will suffer an excise tax that is like adding. we're not likely to do on the retirement-savings side because people aren't saving enough for retirement anyway. we don't want to do anything that will discourage them from putting more money in the accounts. >> reporter: we could have spent the entire week in washington itemizing tax breaks, of course. child credit. earned income tax credit. special rates for dividends and capital gains. but time is short. so we ended our tax tour here with the last often heard solution. >> one proposal we've been hearing more about is simply capping deductions. $25,000. $50,000. anything beyond that, you can't deduct. what does that do and how does that work? >> reporter: the problem with capping the deductions rather than getting rid of them entirely is you lose a lot of revenue. capping at $25,000 loses almost half the revenue you'd get by getting rid of this deduction completely. capping it $50,000 loses almost a third. there's jus